a(n) = a(n-1) + a(n-3), with a(0) = a(1) = 1, a(2) = 5.

Terms

a(0) =1a(1) =1a(2) =5a(3) =6a(4) =7a(5) =12a(6) =18a(7) =25a(8) =37a(9) =55a(10) =80a(11) =117a(12) =172a(13) =252a(14) =369a(15) =541a(16) =793a(17) =1162a(18) =1703a(19) =2496a(20) =3658a(21) =5361a(22) =7857a(23) =11515a(24) =16876a(25) =24733a(26) =36248a(27) =53124a(28) =77857a(29) =114105